The hydrolytic mechanism of both human and bovine pulmonary angiotensin converting enzyme will be examined. As a first step the occurrence of a possible acyl-enzyme intermediate will be examined. The esterase activity of the enzyme will also be studied using benzoyl-glycl-phenyllactyl-leucine as the ester substrate. The effect of the endothelial plasma membrane on the properties of the enzyme will be examined by comparing solubilized enzyme to that bound in purified endothelial plasma membrane. Finally, serum levels of the enzyme in sarcoidosis and other pulmonary diseases will be measured to assess the diagnostic and prognostic value of the serum levels in lung diseases.